During operation of an internal combustion engine, it is desirable to control the formation and emission of certain gases, such as the oxides of nitrogen (NO.sub.x). One method of achieving this result is the use of EGR which is a process whereby exhaust gases are selectively routed from the exhaust manifold or manifolds to the intake manifold of the internal combustion engine. The use of EGR reduces the amount of NO.sub.x produced during operation of the internal combustion engine. In particular, NO.sub.x is produced when nitrogen and oxygen are combined at high temperatures associated with combustion. The presence of chemically inert gases, such as those gases found in the exhaust of the engine, inhibits nitrogen atoms from bonding with oxygen atoms thereby reducing NO.sub.x production.
An EGR system requires a valve assembly that selectively advances exhaust gases from the exhaust manifold to the intake manifold. Typical automotive EGR valves are actuated using the engine's vacuum system. A drawback to using these types of EGR valves in heavy machinery, such as construction equipment, is that many types of heavy machinery do not have suitable vacuum systems similar to those found in automobiles.
Another drawback in EGR valves found in automobiles is that these types of EGR valves produce a limited force. Engines used in heavy machinery can be several times larger than engines used in automobiles. Hence, the force required to open an EGR valve in an internal combustion engine used in heavy machinery is much greater than the force required to open an EGR valve in an automobile.
However, some types of heavy machinery have fuel injectors which utilize a hydraulic fluid to inject fuel into the combustion chamber. In particular, engine oil is pumped to a high pressure, typically 600 to 3000 psi by an injector oil pump. The pressurized oil drives a piston that forces fuel from the fuel injector to the combustion chamber. The high pressure volume generated by the injector oil pump exceeds the volume required to operate the fuel injector during certain engine operating conditions thereby leaving adequate surplus oil volume to actuate an EGR valve.
A drawback with using pressure that has been supplied by the injector oil pump is that this pressure varies considerably. In particular, the engine control module is configured so that changing engine operating conditions cause the injector oil pump to generate varying output oil pressure to meet the needs of the fuel injector. Thus, the pressure output from the injector oil pump is non-uniform.
What is needed therefore is an apparatus and method for selectively routing EGR gases which overcome one or more of the above-mentioned drawbacks.